Conventional gas turbine power plants have large and costly intake air cleaners to remove dust and particles which would normally erode the compressor blades and turbine nozzles. The filters require frequent servicing and also impose a pressure drop in the air stream which reduces air density entering the compressor. The lower density air diminishes the power output of the system, reducing the overall efficiency of the gas turbine cycle, causing more fuel to be consumed per unit of delivered power. One means of compensating is to increase air density by cooling the air. Not only is the density of cool air increased, making the system more efficient, but combustion occurs at a lower temperature, resulting in the emission of less oxides of nitrogen (NO.sub.x). Such cooling has been attempted with direct evaporative coolers which cool air by adding moisture. However, as entrained moisture evaporates, dissolved salts in the water precipitate out forming entrained dust which can erode the gas turbine parts. Other possible ways of cooling the air to increase air density such as refrigerating the air are too energy intensive to be cost effective.
This invention provides cooled, high density air at a reasonable cost that is free from particulate matter. Air is first filtered through a simple low resistance filter screen designed to remove large particles from the intake air stream. It then passes through the dry side of an indirect evaporative heat exchanger where it is sensibly cooled. Embodiments of this type of a heat exchanger are described in U.S. Pat. No. 4,023,949 by Schlom et al. Such a heat exchanger is provided with heat exchange walls having opposite exposed surfaces defining wet and dry sides. Water is applied as extended films across the wet side surfaces. Working air flowing past the water film evaporates portions of the water, cooling the water which cools the dry side by thermal conduction. The grossly filtered air stream passing through the dry side of the indirect evaporative heat exchanger is thereby sensibly cooled without added moisture. The dry cool air stream is then subjected to a fine spray of distilled water which serves to further cool the air stream, clean the air and thoroughly saturate it.
The distilled spray water is obtained from an evaporator heated by the hot turbine exhaust gases. The steam from the evaporator is passed to a condenser, and the purified water is sprayed into the inlet air. The condenser can be cooled by the cool moist air rising from the wet side of the indirect evaporative heat exchanger.